You can buy 3rd party games from Origin too. Batman, Saints Row etc (Sometimes they can be cheaper than Steam, other times not).There are similar services to Steam, such as Origin by Electronic Arts, however, Origin is exclusive to EA games, whereas Steam distributes games from many different developers. In recent times Origin has made some of its games exclusive to Origin so you cannot buy them on Steam, like Battlefield 3, Mass Effect 3, Crysis 2 and others.
.
IIRC, the games which were pulled from Steam weren't cause EA were beign gay, but rather cause Steam was requiring sringent rules on pDLC which no other DD provider required.
For example, you can buy Bf 3 on Gamersgate : http://www.gamersgate.co.uk/DD-BF3UK/battlefield-3-uk
and Gamefly:
http://www.gamefly.com/Download-Battlefield-3/157840/#.T2yWzNmHN_g
Correct me if I'm wrong ofc.
Edit- there are still a lot of EA titles stil lavailable on Steam. Alice: MAdness Returns, beign the onyl one I can think of from the top of my head.